1. Field of the invention
This invention relates to a novel solution spinning process for preparing useful fiber of arylene oxadiazole/arylene N-alkylhydrazide copolymers. The fiber is particularly useful in reinforcing applications such as in tire cord.
2. Description of the prior art
Imai, Journal of Applied Polymer Science, Vol. 14, pages 225-239 (January, 1970), describes solution spinning of p-phenylene oxadiazole/m-phenylene oxadiazole copolymers from sulfuric acid solutions thereof into fiber and that similar attempts to solution spin poly-p-phenylene-1,3,4-oxadiazole from sulfuric acid solutions into useful fiber were unsuccessful.
U.S. Pat. No. 3,536,651 teaches the preparation and conversion of poly(terephthalic hydrazide) fiber to poly-p-phenylene-1,3,4-oxadiazole fiber by using the process described in U.S. Pat. No. 3,238,183, that is, by heating the polyhydrazide fiber to effect intra-linear dehydration-cyclization of the hydrazide moieties to oxadiazole moieties. According to the patent disclosures poly(terephthalic hydrazide) polymer is prepared in an N-substituted amide solvent, such as hexamethylphosphoramide, and is solution spun into fiber using dimethyl sulfoxide as the spinning solvent.
U.S. Pat No. 3,642,708 teaches a process for the fabrication of shaped articles of poly-p-phenylene-1,3,4-oxadiazole by using as a precursor an oxadiazole-N-methylhydrazide copolymeric resin. The resin is allegedly prepared in fuming sulfuric acid and is stated to be significantly more soluble in common N-substituted amide solvents than is poly-(terephthalic hydrazide). The process involves shaping an article of the copolymeric resin using a solution of the resin in an organic polar solvent, then removing the solvent by drying and finally heating the shaped article om betweem 220.degree. C. and 350.degree. C. to convert the N-methylhydrazide units to oxadiazole units: ##STR1##
While the molecular weights (i.e. inherent viscosities) of the p-phenylene oxadiazole-N-methylhydrazide copolymeric resins illustrated in U.S. Pat. No. 3,642,708 are generally satisfactory for the fabrication of films and coatings, they are too low for the fabrication of high tensile strength fiber.